A good summary article of real estate search engines and their design by way of introducing a new player, Roost.
What makes Roost different is that, instead of trying to list all properties in the U.S. as Zillow or CyberHomes do, or take in feeds from individual real estate brokers as Trulia does, it is negotiating with Multiple Listing Services (MLSs) in each metro area to get a comprehensive set of houses on sale. Redfin also taps into the MLS. (The MLS is what real-estate brokers contributeto and use to find homes on the market, and up until recently MLS data was well-guarded from the Web). Roost launches with more than a dozen cities/MLSs, including Atlanta, Boston, Chicago, Dallas, Philadelphia, San Diego, and Washington, D.C. (Notably absent are San Francisco and New York).